Many viruses inhibit the expression of host genes. In most cases the role of the virus-induced inhibition of host gene expression is to inhibit the host antiviral response, particularly the synthesis of type I (alpha/beta) interferons. An important consequence of the inhibition of host gene expression is that it may promote programmed cell death or apoptosis in host cells. The proposed experiments address the mechanisms of inhibition of host gene expression and the consequences of this inhibition for viral induction of an interferon response or induction of apoptosis using the prototype rhabdovirus, vesicular stomatitis virus (VSV). We have established that the viral matrix (M) protein plays a major role in the inhibition of host gene expression by VSV. Aim 1 is to determine the mechanism of inhibition of host transcription by M protein. We have shown that inhibition of host RNA polymerase II-dependent transcription is due to inactivation of the basal transcription factor TFIID. We will determine changes that have occurred in TFIID from infected cells that account for the inhibition using immuno-affinity purified, epitope-tagged TFIID. Aim 2 is to determine the mechanism by which M protein regulates type I interferon gene expression in host cells. We will determine the extent to which M protein inhibits interferon gene expression by inhibition of basal transcription factors, upstream activators of interferon gene expression, or nuclear-cytoplasmic transport of interferon mRNA. Aim 3 is to determine the mechanism by which M protein regulates induction of apoptosis in host cells. We have established that M protein is a potent inducer of apoptosis when expressed in the absence of other viral components. However, there are at least two VSV components that contribute to induction of apoptosis in the context of a virus infection. We will analyze the molecular components involved in activation of apoptosis by M protein and the other viral component. Infectious VSV cDNA clones will be used to identify other viral components involved in the induction of apoptosis by mapping the sequences of previously isolated viral mutants that enhance their ability to induce apoptosis. These experiments will provide a clearer understanding of the molecular basis for viral pathogenesis including the mechanism for the inhibition of host transcription, the inhibition of interferon production, and the activation of apoptosis. [unreadable] [unreadable]